Suggestion: support ClassExpression (as per ES6)

[fsoikin]

The ES6 definition of the "class" construct has the concept of "class expression" - i.e. class definitions may be used as values, such as:

var obj = new (class { x = 5; });
var cls = class { x = 5; };
var cls2 = class extends cls { y = 6; };
var obj2 = new cls2();
// and so on

Sadly, this support is absent in the current TypeScript compiler (I'm using the 9.2 branch) - that is, the above examples would not compile.

Aside from TS team's own argument of "closely aligning with the ES6 specification", this support would enable many useful scenarios for which I currently have to fall back to "any-typed" plain JavaScript.

Here are a few examples of such scenarios which I actually use in my daily work:

1. Returning a class (not object) from a function. With TypeScript, it is currently possible to describe the return type of such function, but not to actually write its body using the "class" construct.
2. "Bind" a class - similar to "binding" a function, i.e. produce another class with certain constructor parameters bound to specific values.
3. Declare a "private" class within the body of a function or within another class.

[danquirk]

This is definitely on the docket. We've talked about it in some design meetings already but do not yet have a full proposal.

[RyanCavanaugh]

Duplicate #239